I couldn't get Windows to allow open with Irfanview always.
Go here and get the reg repair
https://www.winhelponline.com/blog/cant-associate-jpg-png-files-default-apps/
ShareX Set To Irfanview
I like ShareX to open a snip with IrfanView. Sometimes when updating, I lose that setting. This is one way to restore it. What likely change...
